Some of the old cylinder heads Longman etc. seem to have differnent valve sizes for the same application.
What would be the difference between a 37/29.4 and a 35.6/31 head?
I'd guess that the valve size ratio was somwhat ideal at a given ratio?
Let's assume that porting was done "correctly" on both.
Valve sizes
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Vegard
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Astro
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Re: Valve sizes
Hi,
a big inlet and small outlet will have less torque but be better on high revs. My problem was always, how a 37 inlet will do with a 1290. There is not much place to the wall.
a big inlet and small outlet will have less torque but be better on high revs. My problem was always, how a 37 inlet will do with a 1290. There is not much place to the wall.
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ianh1968
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Re: Valve sizes
I would ask how big the 37's are anyway? - Many valves sold as 37mm
are actually 1&7/16" (1.4375") which is 36.51mm...
My guess is that the sizes has as much to do with preventing heads from
cracking between the valves as it does flow ratios.
People like big inlets and the easiest way to get this is to use the smaller
exhaust valves.
To go bigger on the inlets without re-pitching the valves may require
the exhausts to be reduced to prevent a trashed head from being the
result.
The original 'S' heads were 1&13/32" inlet 1&7/32" exhaust (1.40625"/1.21875")
or 35.6mm/30.95mm in French...
Because of head cracking and other issues, BMC reduced the exhaust to
1&5/32" (1.15625") or 29.4mm on the MkIII 'S' and non 'S' heads.
are actually 1&7/16" (1.4375") which is 36.51mm...
My guess is that the sizes has as much to do with preventing heads from
cracking between the valves as it does flow ratios.
People like big inlets and the easiest way to get this is to use the smaller
exhaust valves.
To go bigger on the inlets without re-pitching the valves may require
the exhausts to be reduced to prevent a trashed head from being the
result.
The original 'S' heads were 1&13/32" inlet 1&7/32" exhaust (1.40625"/1.21875")
or 35.6mm/30.95mm in French...
Because of head cracking and other issues, BMC reduced the exhaust to
1&5/32" (1.15625") or 29.4mm on the MkIII 'S' and non 'S' heads.